Method and apparatus for producing cast coated paper



Dec. 21, 1965 J. w. SMITH 3,224,897

METHQD AND APPARATUS FOR PRODUCING CAST COATED PAPER Filed Aug. 19, 1960 COA N WEB CASTING ROLL COAGULANT BATH CONTAINING RELEASE AGENTS WINDER ROLL FIG. 2

IN VEN TOR.

JOHN W. SMITH BY A TTORNE Y United States Patent M 3,224,897 METHQD AND APPARATUS FOR PRODUCENG CAST COATED PAPER John W. Smith, Chillicothe, Ohio, assignor to The Mead Corporation, Dayton, Ohio, a corporation of Ghio Filed Aug. 19, 1960, Set. No. 50,635 7 filaims. (Cl. 3111-64) This application is a continuation-in-part of application Serial No. 648,227, filed March 25, 1957, now US. Patent No. 2,950,214, dated August 23, 1960.

This invention relates to a process for producing high gloss cast surfaced mineral coated papers, and more par ticularly to apparatus which provides coat weight control, coat weight level as well as outstanding smoothness of the coated surface and coverage of the rawstock for practicing the process.

In general, cast-surfaced coated papers are coated with pigment coatings in aqueous dispersion. And known commercial apparatus used in processes for applying these coatings includes a plurality of rolls arranged in various configurations. However, such roll coating apparatus has a commonly recognized deficiency in the fact that the fluid coating is split in the application nip where the paper is separated from the roll after coating, and this splitting of the coating produces a rough, piled surface which, even after a casting operation, exhibits objectionable surface defects.

Numerous unsuccessful attempts have been made to correct this deficiency by adopting so-called standard reverse roll processes used for applying pigmented printing coatings to paper on large scale machine operations. But the inability to meter the thin films required to produce the desired weights of pigmented coatings appears to be the crux of the problem. When using Water system as in cast coating operations, where surface tension forces are higher than in organic solutions, and when the film thickness on the casting roll becomes too thin, or when the casting roll is run too slowly with respect to the paper backing roll, and when the coating color viscosity is low at the same time, or is too low per se, the film on the surface of the casting roll tends to become unstable. Surface tension forces cause the film to buckle or draw into droplets, and the coating applied to the web is non-uniform in thickness or is actually discontinuous.

Further limitations of conventional reverse roll coaters used in processes of making mineral coated paper involve diificulties in fabricating metal roll surfaces, and in providing supports for the rolls with suificient precision to meter the necessary thin films for cast coating. For example, in metering a film 0.010 inch thick, which is the proper range for functional coating, a variation of 0.001 inch represents only 10 percent. The same variation would be 100 percent of a film only 0.001 inch thick, which is the range used for pigmented coating. So thin are the films of normal pigmented coatings, that even localized variations in the temperature of the faces of two metal metering rolls produce significant changes in the meter film thickness. Moreover, known present forms of reverse roll coaters are only adapted to narrow deckles because of film thickness difference caused by sagging of the rolls between supports when the supports are very far apart. A further limitation of standard reverse roll coaters is that grit is able to lodge in the metering nip and cause scratches in the coating applied to paper. And since limitations are always present when applying desired low coat weights needed for acceptable printing coatings, reverse roll metering systems have not heretofore been considered acceptable for producing high gloss cast surfaced mineral coated paper.

In accordance with the present invention, a reverse roll 3,224,897 Patented Dec. 21, 1965 coating apparatus is provided for the process of making cast surface mineral coated paper, which apparatus provides an adequate and unexpected metering system. Moreover, it has been found that such a system is capable of producing on the casting roll stable, thin films from high solids, viscous mineral coating compositions, over a wide range of coat Weights, without restricted deckle, and With freedom from grit defects. In the practice of this invention, the highly viscous, high solids coating compositions have the effect of stabilizing thin films: so that surface tension cannot produce irregularities in thickness of the film on the cating or applicator roll. Moreover, film stability on the applicator roll is required and obtained by this invention whereby a smooth coating is applied to the paper.

While conventional reverse roll metering systems cannot use high solids viscous colors because of the excessively high coat weights which would result, the metering system of this invention is adapted to such colors. And the metering system of this invention when combined with a reverse turning applicator roll to continuously apply the coating composition to a paper web without splitting the film is believed to represent a paramount advance in the art.

Accordingly, it is an object of the present invention to utilize a reverse roll coater system in the production of high gloss cast-surfaced mineral coated paper.

It is a further object to provide such a reverse roll system which insures precise coat weight control, unrestricted coat weight level and excellent smoothness of the coated surface and coverage of the rawstock.

Another object is to provide a metering system which is adapted for metering high solids viscous material coating compositions and can be used with a reverse turning applicator roll to apply the coating to paper without splitting the coating film.

It is a further object to provide a metering system for the production of high gloss cast-surfaced mineral coated paper, which system is capable of producing on the casting roll stable, thin films of high solids, viscous coating colors, over a wide range of coat weights, without undue sensitivity to changes in the position of the rolls, with unrestricted deckle, and with freedom from grit deflects.

Numerous other objects of this invention will more fully hereinafter appear.

In the drawings, which illustrate apparatus embodying, and found satisfactory for practicing and eifectuating the inventions hereof FIGURE 1 is a diagrammatic view in side elevation showing apparatus constructed in accordance with and for carrying out the practicing of the present invention; and

FIGURE 2 is a modification of the coating apparatus used for carrying out the practicing of the present invention.

As shown in FIGURE 1, the paper web to be coated is drawn from roll 10 of suitable paper base stock, and the web 11, is led over guide rolls 12 and 13 to pass through the apparatus in the coating color applying zone. In the modification of FIGURE 1, the web passes through the nip of the coating application rolls 14, 15 where a predetermined amount of coating suspension is applied thereto and distributed with sutficient uniformity over the web surface to give the desired weight of coating material per unit area on the web.

The coating color is fed through a suitable supply line and by suitable means to one or more discharge pipes or nozzles 23 and into the nip between roll .15 and metering roll 24 which have the direction of rotation as indicated, the color forming a pool 25. Doctor 26, as shown, functions to maintain the pool in the nip between rolls 15 and 24 and any well known doctoring means may be employed.

The coated web is then brought with the coated side out tightly around roll 16 which dips into a coagulant and release agent both contained in a tub 17 as described in co-pending Smith application, Serial No. 648,227 filed March 25, 1957, now US. Patent No. 2,950,214. The coated paper 11 is then transferred by press roll 18, after the coating has been formed into a non-tacky tough deformable gel, into nip 19, and thereafter into contact with apparatus referred to, when using somewhat lower solids content colors with greatly reduced viscosity and corresponding increased fiowability, has been very satisfactory in applying the desired quantity and uniform distribution of coating material to the paper web, and of leaving a surface which is sufiiciently smooth so that it may be subsequently coagulated and dried on a finishing surface to give the desired high gloss coated paper. In the latter case, rolls 15, 24 are preferably operated at a low pressure of the order of pounds per lineal inch, or lower and a heated finishing roll 20 having a smooth casting sur- 10 may even be operated at a gap amounting to as much face. The coating on web 11 remains in contact with as .005 inch. casting roll 20 until the coating spontaneously releases Again, referring to the coating apparatus illustrated, therefrom after it has substantially dried and is removed very satisfactory results have been attained when rolls 14 by tension roll 21 to winder roll 22. 15 and 15 were rubber covered rolls; roll 14 having a plas- In order to apply the desired quantity of coating tometer reading of about 136 P. & I. and roll 15 having smoothly to the web, the color solids are preferably a plastometer reading of about 112 P. & J. Rolls 14 and adjusted so that the coating is not too viscous for easy 15 may be operated with a pressure therebetween varyapplication, nor so dilute as to be incapable of forming ing during operation, for example, from about 1 to 25 a tough gel. Relatively high solids content coating suspounds per lineal inch, with satisfactory results having pensions, e.g. of the order of 45 %-65 solids or more, been obtained at a pressure of preferably about 10 pounds have been used successfully and, as a general rule, the per lineal inch. Roll 24 in this connection was a hard preferred percentage of solids in the coating is governed surfaced Stonite roll. Rolls 18 and 21 had plastometer by the type and quantity of adhesive selected for the color readings of 65 and 32 P. & J. respectively, while roll 20 as set forth in the Smith application, supra. 25 was a metal roll, having a smoothly buffed methyl silicone The coating apparatus shown in FIGURE 1 of the casting surface, such as disclosed in co-pending applicadrawing is a reverse roll system which has been found tion, supra. Roll 16 was a corrosion resistant roll such to be very satisfactory and effective for transferring from as stainless steel. More generally, however, it has been the trough of coating material or so-called coating color, found that rolls 14-, 15 and 24 may all be resilient surface between rolls 15 and 24, accurately controlled amounts of type rolls, such as rubber covered rolls having a plastomthe coating material. With the high solids content coateter reading of the order of 80 to 140 P. & I. when measing colors of the order of as high as 65% solids, which ured wi h a /s inch ball. And if one or more of these in their normal condition are substantially non-flowable, rolls is hard surfaced, i.e., of metal, Stonite, or the like, this apparatus, with the rolls under considerable pressures then its adja n r is preferably resilient surfa P I of the order of 10 to 100 pounds per lineal inch, and with example, the following combinations of these coating roll 24 being operated at 0.10.5 times the speed of applimechanism rolls have been found commercially suitable cation roll 15 which was turned at from 1.38-3.00 times and are presented in illustration but not in limitation of the speed of the paper web 11, effects a large temporary the invention.

Type of Roll by Combination Roll No.

14 Metal 140 P. &J 136 P. &.T so P. &J 140 P. &;r 15 112 P. & Metal 112 P. & 130 P. & Stonite 24 Metal 112 P &J Metal 112 P. &J 112 P. &J

change from its normal condition of non-flowability, caus- All plastometer values were measured with a /8 inch ing it to become readily fluent and tlowable so that it may 59 P. & J. ball. Whenever the surface of the application be thus accurately controlled as to quantity and general roll 15 is provided with a resilient cover, as in Examples distribution. The coating material passing in controlled 1, 3, and 4 above, it is desirable to operate the coater amount through the nip of the rolls 15, 24 is carried on in a manner such that the film of coating on roll 15 is the surface of the roll 15 as it travels up toward the only partially transferred to the web of paper, and the paper web, to transfer the desired quantity of coating excess serves as a lubricating layer to prevent excessive material for the predetermined coat weight desired, and drag between the paper web and the surface of roll 15. in such condition of flowability that the color will be The presence of this lubricating layer is a normal occurgenerally distributed across the surface of the roll 15 as it rence under the operating conditions previously specified. moves toward the paper and application nip of rolls 15, The pressure in operation between rolls 18 and 20 14. In such condition of flowability and such distribu- 60 may be varied over a substantial range; for example, tion that when brought in contact with the paper web by from about 200 to 600 pounds per lineal inch, with satisroll 15 turning in a direction opposite to the direction of factory results having been obtained at a pressure of travel of the paper web, there will be transferred to the about 400 pounds per lineal inch. In this connection, it web a substantially uniformly distributed layer or film of has been found that the upper pressure limit is detercoating material which is of considerable and unexpected mined by the strength or toughness of the gelled coating. smoothness. The coating materials commonly used, con- And the pressure between rolls 1S and 20 may be varied tain a substantial amount of adhesive material such as over wide limits so long as sufficient pressure is used to casein. However, by the disclosed reverse roll system, .insure intimate contact between the coating surface and there is suflicient Working of the coating color both before the casting surface. it passes into the application nip of the rolls 14, 15, and Various coating materials may be employed in practicalso within the nip by reason of the reverse turning of ing the present invention and as indicated by the formularoll 15, so that even high solids content coating colors tions hereinafter set forth, the coating material generally will be made sufficiently fluid, for securing the desired comprises a mineral and an adhesive in aqueous medium. accurate coat weight and the uniform distribution of the 5 Both the adhesive content and the total solids content of film upon the surface of the paper web. Moreover, the

the coating materials to be used are predicated on the ultimate high gloss coated paper desired and for highly satisfactory operations, such adhesive and total solids content may be somewhat critical. For example, it has been found that the preferred range of adhesive contents is of the order of 12%20%, although more or less adhesive can be used if special end-use requirements of the ultimate high gloss paper product so dictate. Moreover, if starch is used in admixture in the adhesive, more total adhesive is required than if it is not so used. Generally, the higher region of the adhesive content range is useful in preparing papers for oifset printing, while the lower range has been found useful for letterpress printing.

A color formula which has been found to function satisfactorily in the practicing of the invention is of the following composition, wherein the parts by weight are taken on a,dry basis:

Example I Parts by weight Clay (English coating clay) 42.0 Calcium carbonate 42.0 Casein (Argentina) 12.0 Caustic soda (parts per 100 parts of casein) 6.0 Sodium pyrophosphate 0.75 Calcium stearate 0.5

Dow 512-R latex (butadiene-styrene copolymer Di isobutylphenoxyethoxyethyldimethylbenzyl ammoniumchloride, monohydrate (Hyamine 1622, Rohm & Haas Co.) 0.05

Such color gives satisfactory results in the practicing of this invention when admixed with water to have a solids content of approximately 50.5%.

The following examples of color formulations which have likewise been used satisfactorily are set for purposes of illustration, but not of limitation. The parts by weight of these compositions are taken on a dry basis:

Example II Parts by weight Clay (English coating clay) 42.0 Calcium carbonate 42.0 Soya protein (refined) 12.0

Ammonia-26 B (parts per 100 parts of protein)" 12.0 Dow 512-R latex 4.0 Sodium pyrophosphate 0.75 Calcium stearate 0.5 Hyamine 1622 0.05

Example III Parts by weight Clay (English coating clay) 38.0 Calcium carbonate 41.0 Satin white 5.0 Alpha protein 12.0

Ammonia-26 B(parts per 100' parts of protein) 12.0

Dow 512-R latex 4.0 Sodium pyrophosphate 0.75 Calcium stearate 0.5 Lignasan 0.05

Example IV Parts by weight Clay (English coating clay) 51.0 Calcium carbonate 30.0 Alpha protein 18.0 Azite (dicyandiamide) (parts per 100 parts of protein) 25.0 Ammonia-26 B (parts per100 parts of protein) 12.0 Sodium pyrophosphate 0.75 Calcium stearate 0.5 Lignasan 0.05

Example V Parts by weight Calcium carbonate 84.0 Alpha protein 12.0

Ammonia-26 B (parts per 100 parts of protein) 18.0

The surface temperature of the casting drum 20 which preferably is a chromium surfaced roll and is preferably from C. to 101 C. during the drying cycle for producing the cast-surfaced coated paper having unusually high brightness and opacity and high gloss of this invention, although temperatures ranging from 65 C. to as high as 105 C. have been used without harmful results. It has been found that temperatures approaching -101" C. are advantageous when the more active coagulants are employed.

In the coater modification shown in FIGURE 2, rolls 32 and 33 form the metering pair of the coater. One or both of these rolls are provided with a resilient surface, such as a rubber cover. They may be operated at equal speeds, or roll 33 may be rotated more slowly than roll 32. They rotate in opposite angular directions, as indicated by arrows and the pressure between these rolls is controllable. When a film of coating from pool 34 is metered between rolls 32 and 33, a portion of this film follows the face of roll 32 into contact with roll 31 where it is blended in the nip formed by rolls 31 and 32. Roll 31 may be operated more slowly, equal to or faster than roll 32, and is preferably operated with a surface speed greater than that of roll 30.

Roll 31 can be made of rubber or some other resilient material, but preferably, it has a hard, abrasive-resistant surface, such as brass, chromium or Stonite. Roll 31 transfers a part of the coating from the face of roll 32 and applies it to the paper Wrapping roll 30, with a wiping action. The surface of roll 31 must be relatively smooth in comparison to the thickness of the film it carries. And, if desired, a smoothing device 35 such as a flexible distributor or a spread shaft may be installed in the position shown in FIGURE 2, so that it lightly contacts the surface of roll 31 and smoothes the coating on this surface. If a shaft is used instead of a spring steel type distributor, it should be made of a material permitting satisfactory contact with the surface of roll 31. For example, if roll 31 has a hard surface, the spread shaft should be ru bber covered. Such a smoothing device, while not always necessary, may be desirable in cases where the film pattern produced by the splitting of the wet film in the hips between rolls 32 and 33 or between rolls 31 and 32 is being transferred with out adequate blending to the paper in the nip between rolls 30 and 31.

It has been found that the coater described and shown in FIGURE 2 of the drawing, provides a unique combination or precise coat weight control, unrestricted coat weight level and excellent smoothness of the coated surface and coverage of the rawstock in the production of high gloss cast-surfaced mineral coated papers.

While the methods, apparatus and products herein described are for the purpose of illustration only, it is to be understood that the present invention includes all modifications and equivalents which fall within the scope of the'invention which is defined by the appended claims.

What is claimed is:

1. Web coating apparatus comprising a coating roll, means for conveying a web to be coated to and from said coating roll, a metering roll mounted with the axis thereof in substantially the same horizontal plane as the axis of said coating roll to form with said coating roll a metering nip, means for maintaining a pool of coating material adjacent an upper nip formed by the contact relationship of the metering and coating rolls, at least one of said rolls forming said metering nip being resiliently surfaced, said rolls being in abutting relation under a pressure of the order of to 100 pounds per lineal inch, means for rotating said rolls in the same predetermined angular direction to cause relative reverse rotation of said rolls and also to cause the surface of said coating roll to move upwardly in a direction op posite to the direction of the web.

2. Web coating apparatus comprising a coating roll, means for conveying a web to be coated to and from said coating roll, a metering roll mounted with the axis thereof in substantially the same horizontal plane as the axis of said coating roll to form with said coating roll a metering nip, means for maintaining a pool of coating material adjacent an upper nip formed by the contact relationship of the metering and coating rolls, at least one of said rolls forming said metering nip being resiliently surfaced, said rolls being in abutting relation under a pressure of the order of O to 100 pounds per lineal inch, means for rotating said rolls in the same predetermined angular direction to cause relative reverse rotation of said rolls and also to cause the surface of said coating roll to move upwardly in a direction opposite to the direction of the web and in wiping contact therewith.

3. Web coating apparatus comprising an applicator roll, a backing roll forming an application nip with said applicator roll, and said application nip adapted to pass therethrough a web to be coated, a metering roll mounted with the axis thereof in substantially the same horizontal plane as the axis of said applicator roll to form with said applicator roll a metering nip, means for maintaining a pool of coating material above said metering nip, said rolls being in an abutting relationship under a pressure of the order of 0 to 100 pounds per lineal inch, one of said rolls forming said metering nip having a resilient surface, one of said rolls forming said application nip having a resilient surface, means for rotating said rolls in the same predetermined angular direction to cause relative reverse travel of the surfaces thereof and to cause said surface of said applicator roll to move in the direction opposite the direction of the web.

4. Web coating apparatus comprising a plurality of rolls, said rolls forming a metering nip, a blending nip and an application nip, said application nip adapted to pass therethrough a web to be coated, said rolls forming said metering nip being in abutting relationship and under a pressure of the order of 0 to 100 pounds per lineal inch, at least one of said rolls forming said metering nip having a resilient surface, means for maintaining a pool of coating material above said metering nip, means for rotating said rolls forming said blending nip in the same predetermined angular direction, means for rotating said rolls forming said application nip in the same predetermined angular direction to cause relative reverse travel of the surfaces thereof.

5. A process for producing cast-surfaced mineral coated paper wherein a continuously moving web of paper is smoothly and evenly coated with a coating suspension which is later brought to a high gloss by passing the 8 coated web over and in intimate contact with the surfac of a finishing roll, which comprises, prior to casting: applying a mineral-adhesive coating suspension having from about 45% to about total solids to a pressure nip formed between the surface of a metering roll and the surface of an applicator roll, the pressure between said rolls being of the order of 0 to pounds per lineal inch, and at least one of said rolls having a resilient surface, said metering roll and said applicator roll moving in the same angular direction, said applicator roll surface en-' gaging said web and moving in the opposite direction thereto, transferring a portion of said coating suspension from said applicator roll to said web while retaining a portion thereof on said moving applicator roll surface whereby a lubricating film of said coating is maintained on said applicator roll surface.

6. A process for producing cast-surfaced mineral coated paper wherein a continuously moving web of paper is smoothly and evenly coated with a coating suspension which is later brought to a high gloss by passing the coated web over and in intimate contact with the surface of a finishing roll, which comprises, prior to casting: applying a mineral-adhesive coating suspension having from about 45% to about 65% total solids to a pressure nip formed between the surface of a metering roll and the surface of an applicator roll, one of said rolls having a hard surface and the other of said rolls having a resilient surface, said metering roll and said applicator roll moving in the same angular direction, said applicator roll surface engaging said web and moving in the opposite direction thereto, transferring a portion of said coating suspension from said applicator roll to said web while retaining a portion thereof on said moving applicator roll surface whereby a lubricating film of said coating is maintained on said applicator roll surface.

7. A process for producing cast-surfaced mineral coated paper wherein a continuously moving web of paper is smoothly and evenly coated with a coating suspension which is later brought to a high gloss by passing the coated web over and in intimate contact with the surface of a finishing roll, which comprises, prior to casting: applying a mineral-adhesive coating suspension having from about 45% to about 65 total solids to a pressure nip formed between the surface of a metering roll and the surface of an applicator roll, one of said rolls having a hard surface and the other of said rolls having a resilient surface, the pressure between said rolls being of the order of O to 100 pounds per lineal inch, said metering roll and said applicator roll moving in the same angular direction, said applicator roll surface engaging said web and moving in the opposite direction thereto, transferring a portion of said coating suspension from said applicator roll to said web while retaining a portion thereof on said moving applicator roll surface whereby a lubricating film of said coating is maintained on said applicator roll surface.

References Cited by the Examiner UNITED STATES PATENTS 1,508,720 9/1924 Perry ll7--64 2,157,212 5/1939 Moore 117111 2,185,859 1/1940 Massey 1l7-111 2,199,228 4/1940 Obenshain et a1 1l764 2,252,345 8/1941 Johnson 1l764 2,678,890 5/1954 Leighton 1l764 2,829,980 4/1958 Redd 11764 2,842,092 7/1958 Pomper 117lll X 2,870,738 l/1959 Jacobs et al. 118-249 2,919,205 12/1959 Hart 1l7-64 WILLIAM D. MARTIN, Primary Examiner.

MURRAY KATZ, RICHARD D. NEVIUS, Examiners. 

3. WEB COATING APPARATUS COMPRISING AN APPLICATOR ROLL, A BACKING ROLL FORMING AN APPLICATION NIP WITH SAID APPLICATOR ROLL, AND SAID APPLICATION NIP ADAPTED TO PASS THERETHROUGH A WEB TO BE COATED, A METERING ROLL MOUNTED WITH THE AXIS THEREOF IN SUBSTANTIALLY THE SAME HORIZONTAL PLANE AS THE AXIS OF SAID APPLICATOR ROLL TO FORM WITH SAID APPLICATOR ROLL A METERING NIP, MEANS FOR MAINTAINING A POOL OF COATING MATERIAL ABOVE SAID METERING NIP, SAID ROLLS BEING IN AN ABUTTING RELATIONSHIP UNDER A PRESSURE OF THE ORDER OF 0 TO 100 POUNDS PER LINEAL INCH, ONE OF SAID ROLLS FORMING SAID METERING NIP HAVING A RESILIENT SURFACE, ONE OF SAID ROLLS FORMING SAID APPLICATION NIP HAVING A RESILIENT SURFACE, MEANS FOR ROTATING SAID ROLLS IN THE SAME 